Asphalt oxidation

ABSTRACT

A METHOD OF MANUFACTURING OXIDIZED, COATING GRADE ASPHALTS WHEREIN ASPHALT CHARGE STOCKS, SUITABLE AS SUCH FOR USE AS ROOFING FELT SATURANTS AND DIRECTLY OXIDIZABLE TO SHINGLE SATURANTS BUT NOT, WITHOUT BLENDING, DIRECTLY OXIDIZABLE TO SHINGLE COATING ASPHALTS, ARE CONVERTED INTO CHARGES ALSO DIRECTLY OXIDIZABLE TO SHINGLE COATING ASPHALTS. THE METHOD COMPRISES HEATING AT ABOUT 700 TO 775*F. AN ASPHALT RESIDUUM HAVING NEGATIVE OLIENSIS, A FLASH POINT ABOVE 500*F. AND A SOFTENING POINT OF 105*F. TO 115*F., FOR A TIME SUFFICIENT TO GIVE AT LEAST 3 WEIGHT PERCENT CONVERSION TO 950*F. MINUS BOILING RANGE HYDROCARBONS BUT WITHOUT PRODUCING AN ASPHALT HAVING A POSITIVE OLIENSIS, AND OXIDIZING RESULTING ASPHALT STOCK INTO A COATING ASPHALT HAVING A SOFTENING POINT OF 220*F. TO 230*F. AND A PENETRATION AT 77*F. IN THE RANGES OF 16 TO 24.

United States Paten a 3,598,716 ASPHALT OXIDATION Eugene M. Fauber, Hammond, Ind., assignor to Atlantic Richfield Company, New York, N.Y. No Drawing. Filed Apr. 20, 1970, Ser. No. 30,214 Int. Cl. C10g 1/00 US. Cl. 208-6 Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing oxidized, coating grade asphalts wherein asphalt charge stocks, suitable as such for use as roofing felt saturants and directly oxidizable to shingle saturants but not, without blending, directly oxidizable to shingle coating asphalts, are converted'into charges also directly oxidizable to shingle coating asphalts. The method comprises heating at about 700 to 775 F. an apshalt residuum having negative Oliensis, a flash point above 500 F. and a softening point of 105 F. to 115 F., for a time sufiicient to give at least 3 weight percent conversion to 950 F. minus boiling range hydrocarbons but without producing an aspalt having a positive Oliensis, and oxidizing resulting asphalt stock into a coating asphalt having a softening point of 220 F. to 230 F. and a penetration at 77 F. in the range of 16 to 24.

This invention relates to the manufacture of oxidized asphalts suitable for use by roofing manufacturers. More particularly, the invention is directed to a method of converting asphalt residuum charges suitable as such for use as roofing felt saturants into charges directly oxidizable to either shingle saturants or shingle coating asphalts.

It is known that roofing manufacturers use asphalts as roofing felt saturants, shingle saturants and shingle coatings. Each use requires an asphalt of a different grade, that is, one having a particular softening pointpenetration relationship. Typical softening point-penetration relationships established by roofing manufacturers for asphalts which are suitable for use as roofing felt saturants, shingle saturants and shingle coatings are shown in the table below.

Asphalt residuum charges manufactured by vacuum reduction of straight reduced crude mineral oils often already possess softening point-penetration relationships required of roofing felt saturants. These residuum charges can be oxidized to raise their softening points and lower their penetration values to within the relationship values required of shingle saturant asphalts. However, it is well known that the charges cannot be directly, i.e. Without blending with other substances, oxidized to produce asphalts meeting the rather narrow limits in softening pointpenetration relationship required of shingle coating asphalts. For example, when asphalt charges having softening points in the range of about 105 F. to 115 F. are air blown to softening points within 220 F. to 230 F., their penetration falls below the minimum coating grade requirement of 16.

To overcome this problem, it has heretofore been necessary to blend the charge asphalts with light, high melting, microcrystalline waxes and lubricating oils. These blending methods are expensive. The waxes and oils are of considerably higher value than the asphalts used and blending requires manpower and extra equipment. Fur- 3,598,716 Patented Aug. 10, 1971 ice" ther, these methods require roofing manufacturers to have two charges on hand, one being an asphalt suitable as it is for use as a felt saturant and directly oxidizable for use as a shingle saturant, and one to blend with the asphalt to make a charge suitable for oxidation to coating grade requirements.

Now, in accordance with the simple and inexpensive method of this invention, roofing manufacturers need only have one charge stock on hand because straight reduced crude asphalt residuum charge stocks already suitable for use as felt saturants, can now be directly oxidized not only to a shingle saturant but also to shingle coating grade asphalts. The asphalts which may be employed in the method of this invention are straight reduced crude asphalts which cannot be directly oxidized to the softening point-penetration values of the aforesaid ranges required of coating grade asphalts. Straight reduced asphalts are manufactured by vacuum reduction of crude mineral oils, e.g. petroleum reduced crudes or bottoms produced, for instance, by atmospheric distillation. Asphalts obtained in this manner may have a wide range of softening point-penetration-values. It has been found, however, that the asphalts suitable for use according to the method of this invention have the test specifications shown in the table below.

TABLE II Tests: Values Penetration at 77 F.,

ASTM D-S -250 (preferably -200) Softening point (R & B), F. 105-115 Oliensis Spot Test Negative The Oliensis Spot Test determines durability and functional performance of an asphalt and it is essential that the results of the test be negative at all times, i.e. before and after the heating soaking step of the method of this invention. The Spot Test involves dissolving an asphalt sample in naphtha and placing a spot of solution on filter paper. If the stain is non-uniform in color or density, the reading is positive and indicates that the asphalt sample is cracked, overheated or contains sludge or other matter poorly tolerated by the asphalt. If the paper is stained in a uniform, brown, circular manner, the reading is negative. A negative reading assures good functional performance and durability, meaning it will be more likely to resist cracking and hardening with age.

To obtain an asphalt residuum having a negative Oliensis certain precautions are taken during crude oil refining. For example, the temperature at which a crude is discharged from a heater to a processing crude still vacuum tower and the processing time and temperature of the asphalt in the tower are controlled to assure that the products obtained will give a negative result to the Oliensis Spot Test. The asphalt residuum charge stocks employed in the method of this invention preferably have a flash point of at least about 500 F. or at least about 520 F. to prevent fire hazards since oxidation of these charge stocks to roofing grade asphalts is usually carried out at about 500 P.

(An essential step in the method of this invention comprises heat soaking to a controlled extent an asphalt residuum charge stock having the test specifications of Table II, prior to its oxidation to a coating grade asphalt. It has been found, as the data given hereafter will show, the heat soaking the asphalt charge prior to oxidation sufficiently lowers the penetration value of the oxidized asphalt to within the otherwise unattainable range required of coating grade asphalts. Heat soaking also reduces the time required to oxidize the charge to a coating grade asphalt.

Although the time and temperature of heat soaking may vary depending upon the source and nature of the asphalt 4 the heat-soaked, air-blown coating grade asphalt of column D.

TABLE III.EFFECT OF HEAT SOAKING ON PENETRATION VALUES OF AIR-BLOWN ASPHALTS A B C D Heat-soaked Non-heatasphalt residsoakod asphalt uum oxidation Air-blown Air-blown residuum oxiunit charge asphalt coating grade dation unit stock (light (non-heatasphalt Test specifications and air blowing time charge stock ends removed) soaked) (heat-soaked) Penetration, 77 F 175 175 14 17 Softening point (RttB), F 107 107 220 220 Flash, COC, F 610 605 Oliensis Spot Test Negative Negative gig Air blowing time to attain 220 F. softening point, hrs.

and the particular softening point-penetration relationship of the asphalt charge, for an asphalt residuum charge meeting the hereinbefore enumerated required specifications, it has been found that a heat soak at about 700 to 775 F., preferably about 715 to 760 F., for a time sufficient to convert at least 3 weight percent of the asphalt to 950 F. minus boiling range hydrocarbons but without giving an asphalt having a positive Oliensis Test transforms such an asphalt charge which was not capable of being oxidized to a coating grade asphalt into one that is. Often, this conversion to 950 F. minus materials is up to about 7 weight percent, preferably at least about 4.5 percent. The heat soaking may take place in any asphalt heater normally used in crude oil refining. An asphalt produced, for example, from a crude still vacuum tower can be fed to such an asphalt heater and, for example, after heat soaking in the substantial absence of molecular oxygen, the heat-soaked charge can then be fed to another vacuum tower where light materials such as for example propane and butane gases and distillates, e.g. boiling below about 950 F., produced by a combination of temperature and time in the heater and tower can be removed. The remaining improved asphalt oxidation unit charge stock can then be fed to a blowing drum for oxidation to a coating grade asphalt which will meet coating grade test specifications. Oxidation of the charge stock is conducted in the presence of molecular oxygen and at temperatures of about 400 to 550 F., preferably about 475 to 525 F.

The previously mentioned effects of heat soaking upon the penetration values of air-blown asphalts are shown in Table III. The asphalt residuum charge stock (column A) was manufactured by vacuum reduction of reduced crude obtained from a mixture of Mid-Continent and Wyoming crudes. This asphalt residuum was heat soaked for 6 minutes at 748 F. to yield about a 93.3 weight percent heatsoaked asphalt residuum oxidation unit charge stock (column B) and light ends comprising about .7 weight percent gas, about 3.3 weight percent C to 400 F. end point distillate and about 2.7 weight percent 400 F. distilate. The heat-soaked asphalt residuum oxidation unit charge stock of column B was then air blown at a temperature of about 500 F. and an air rate of about 3.3 cubic feet per hour per pound of asphalt charge to produce Table III shows that the asphalt residuum charge stock could not, without heat soaking, be air blown to meet the required softening point-penetration values of coating grade asphalts.

I claim:

1. A method of manufacturing coating grade asphalts by the oxidation of an asphalt residuum charge having a negative Oliensis, a softening point of to F., and a penetration at 77 F. of to 250, the charge being incapable of being directly oxidized to a coating asphalt having a softening point-penetration relationship of a 220 to 230 F. softening point and a penetration at 77 F. of 16 to 24, which comprises heating the asphalt essentially in the absence of molecular oxygen, at about 7 00 to 775 F. to convert at least 3 weight percent to 950 F. minus boiling hydrocarbons but without producing an asphalt having a positive Oliensis Test, and oxidizing by contact with molecular oxygen a charge consisting essentially of asphalt resulting from said heating to obtain a coating grade asphalt having a softening point of 220 to 230 F. and a penetration at 77 F. to 16 to 24.

2. The method of claim 1 wherein the heating in the absence of molecular oxygen is continued to produce about 4.5 to 7 weight percent of 950 F. minus boiling hydrocarbons.

3. The method of claim 2 wherein the temperature of the heating in the absence of molecular oxygen is about 715 to 760 F.

4. The method of claim 3 wherein the asphalt charge has a penetration at 77 F. of to 200.

5. The method of claim 4 wherein the oxidizing is conducted at about 475 to 525 F.

References Cited UNITED STATES PATENTS 2,343,789 3/1944 Morris 2086 3,392,104 7/1968 Potts et a1 2086 3,238,116 3/1966 Hamner et al. 2086 1,513,133 10/1924 Rowland 2086 DELBERT E. GANTZ, Primary Examiner V. OKEEFE, Assistant Examiner 

